1. Field of the Invention
The invention relates to the field of detectors of electromagnetic radiation. In particular the invention relates to the use of a two-dimensional electron gas (“2DEG”) and/or a two-dimensional hole gas (“2DHG”) in the detection of electromagnetic radiation including terahertz frequency radiation, photodetection, and charged particle detection.
2. Description of the Related Technology
Confined electron behavior has ushered in a new era in electronics and photonics. Controlled variation of the energy level spacing and availability of electronic states using geometric or electrostatic confinement of carriers in quantum wells, quantum wires and quantum dots has led to important advances in transistors, diodes, LEDs and Lasers. The realization of systems in which carriers are effectively confined within planes, along one-dimension, in current rings, or through narrow constrictions or islands, has attracted enormous interest. Detailed investigations in mesoscopic systems have uncovered a range of exciting and unique electronic transport properties, including electron cavities, Kondo physics, the Aharonov-Bohm effect, and other effects, including quantum cascade LASERS, phonon confinement, optical phonon confinement, and exciton confinement.
Modulation doping of hetero-structures which allow electrons to be screened from their dopant ions and travel only subject to lattice and external forces has had a tremendous effect on transistor technology with high electron mobility transistors (HEMT) outperforming all others in terms of speed. Introduction of modulation doping in order to produce a dense arrangement of electrons, on the order of 1012 cm−2 electrons in 1979 and, similarly, a dense arrangement for holes in 1984, has been the driving force behind such progress. In these devices, a heterojunction is made between lattice matched wide-gap and narrow-gap material. Doping of the wide-gap material introduces carriers that are transferred to the narrow-gap material and confined to it due to band-gap discontinuity. Two-dimensional clouds of both electrons, i.e. a 2DEG (2 dimensional electron gas) and holes, i.e. a 2DHG (2 dimensional hole gas) have been produced which have become conduction channels for both n-type and p-type HEMT devices.
In a HEMT device, gating of a channel of charge produces a transistor action and the speed of the device is limited by the transit time of the carriers from source to drain. The model used is that of a reservoir-channel-reservoir with the channel consisting of a 2DEG, or a 2DHG, with the reservoirs of electrons being ohmic metals of the source and the drain. Transit of electrons in this 2DEG is expedited since scattering by ionized dopants is removed. It is nevertheless conduction of the channel subject to an electric field that limits the speed.
Thus, there remains a need for a sensor for detecting electromagnetic radiation that can overcome the canonical limitations of drift or conductivity based devices, such as transistors, thereby achieving unprecedented speed and sensitivity. Such a development applies to a wide range of frequencies including frequencies used in photonics applications, to terahertz range frequencies, and to other detection modalities such as charged particle detection.
A new and important task for electromagnetic radiation sensors is the detection of terahertz (THz) radiation. Detection of the terahertz range of the electromagnetic spectrum, as well as other ranges of the electromagnetic spectrum, can play an important role in a variety of different technological and commercial fields. A unique feature of THz frequencies, as compared to shorter wavelengths, is that the ambient background thermal noise almost always dominates the naturally emitted narrowband signals. Therefore, either cryogenic cooling or long integration time radiometric techniques, or both, are typically required. Typically, THz components fall into two categories: sources and detectors. Other components such as waveguides, filters, antennas, amplifiers, and THz materials are also important to THz technology. Terahertz sources are difficult components to realize. The reasons for this include the high frequency roll-off of the electronic solid-state sources, difficulties that tubes face because of metallic losses and scaling problems, and low level photon energies (meV) of solid-state lasers operating at this range, where the energy is comparable to the relaxation energy of the crystal. As far as power level is concerned, frequency conversion techniques, either up from a millimeter wave, or down from the optical and infrared range, have so far been the most successful techniques.
One of the components that has received a lot of attention is the diode frequency multiplier. Varactor diode and Schottky diode multiplier circuits have been introduced multiplying MMW signals up to a few hundred GHz. Recently, a 200 to 2700 GHz multistage frequency multiplier was introduced using Schottky diodes on extremely thin GaAs substrate. A sub-millimeter-wave side band generator consisting of a whisker contacted Schottky varactor mounted in a waveguide is another recent example. This device is a sub-millimeter source with high efficiency and utilizes the pumped nonlinear reactance of the varactor. An output power of 55 μW at 1.6 THz with a conversion loss of 14 dB was reported. Microwave pump power of 20 dBm at 1.8 GHz and a CO2-pumped far-IR laser with 3 mW power at 1.6 THz was used for this demonstration.
Some other methods of THz generation that have been reported by Kolodzey et al. are quantum well inter-sub-band transition in SiGe, boron doped resonant state transition in strained SiGe, and impurity transitions in doped Si. Recently, Shur and co-workers succeeded in obtaining voltage tunable emission of terahertz radiation from a gated 60 nm InGaAs high electron mobility transistor.
U.S. Pat. No. 5,631,489 to Roser discloses use of Schottky contacts for terahertz detectors used at room temperature. In Roser, an antenna is made from a whisker of metal (Au—Ni), and Schottky contacts are made from a platinum-gold alloy. A point contact Schottky diode is used as a heterodyne receiver.
Although the device of the instant invention is based on the formation of a plasma of charge using conventional MODFET technology, one of the distinctions from the devices discussed above is that in the proposed device the 2DEG is maintained in quasi-equilibrium and its perturbations are sensed using terahertz radiation. Using the instant invention's detection devices as high-speed, room temperature THz detectors can overcome one or more of the drawbacks found in the prior art. Furthermore, utilization of a tunable device using a 2DEG can also serve a role in providing fast and reliable detectors of other wavelengths of electromagnetic radiation including optical detectors used in fiber optic communication systems, as well as other modalities such as charged particle detection.
Therefore, there exists a need for detection devices using a 2DEG to improve sensing of terahertz radiation and other electro-magnetic radiation in order to provide viable, highly sensitive, detectors.